In the production of lift-tab can ends, the lift-tabs are made rough-side-up and it is necessary to invert the tabs so that they are positioned smooth side-up, prior to attachment of the tabs to can ends. This inversion has generally been accomplished manually, after the tabs are removed from the strip of metal stock material in which they are formed. It would be desirable, therefore, to provide a method wherein the tab is inverted automatically thereby saving labor.
In my invention, I provide a first press machine which makes the can end and a second press machine, or tab press, which makes the can end lift-tab. A third press machine, or conversion press, is provided which attaches the lift-tab to the can end to form a lift-tab can end. All three of the press machines are separate machines. Can ends are conveyed from the first press to the third press.
My invention does not provide a tab punch disposed at the exit of the tab press to remove the tab from the strip of material from which it is made. This would require inverting each tab prior to attaching it to a can end. Instead, a drive roller is provided on the frame of the tab press that rolls the strip of metal stock material with the formed lift-tabs loosely attached through either a half twist or a half loop to an inverted condition.
With the strip of metal stock material with the formed lift-tabs now inverted by either the half twist or the half loop, the invention provides two alternative methods of getting the lift-tabs into the proper position relative to the can ends for attachment.
The first method involves the running of the strip of metal stock material with the formed lift-tabs loosely attached through a locating means so that the strip will go into the conversion press with the lift-tabs being properly positioned with respect to a can end so that the conversion press may simultaneously detach a tab from the strip and attach the tab to a can end to form a lift-tab can end.
The second method of getting the tabs into working relationship with the can ends is to pass a strip of metal stock material with the lift-tabs formed therein through a tab punching station where a tab punch punches the formed tabs from the strip of metal stock material into at least one lane of formed tabs. A conveyor then conveys the tabs from the punching station to a conversion press. At the conversion press, the tabs are stacked smooth-side up, and a tab ejector is provided for feeding one tab at a time from the stack of tabs into the conversion press. A locating means is also provided for placing the tab into working relationship with a can end so that the conversion press may attach the tab to a can end to form a lift-tab can end.
In accordance with the broader aspects of the invention, any number of conversion presses can be employed. In addition, the invention may be used when lift-tabs are formed in rows or lanes across the width of the strip of metal stock material. In such case, the tabs from each row may be conveyed to a conversion press.
If the invention is practiced using several conversion presses and several corresponding rows or lanes of tabs, there may be times when at least one conversion press is inoperative for some reason. In such event, the tabs which are intended for the inoperative conversion press can be punched from the strip of metal stock material using a separate punch before the strip arrives at the tab punching station of the inoperative conversion press. This allows the tab press and other conversion presses to continue operating while preventing a build up of unnecessary lift-tabs at the inoperative press (or presses).
In the case where the strip of metal stock material is pressed in the tab press so that there are multiple tabs formed across its width, I can insert a commercially-available plasma cutter which will precisely separate the tab strip into individual strips of lift-tabs so that each of these individual strips may be passed through its designated conversion press. If one or more of the conversion presses become inoperative, then the tab strip or strips intended for that press or presses can be taken out of the inoperative press or presses. The tabs may be removed from that strip or strips as described above, and all other presses can continue to run. An alternative scheme involving the routing of separate tab-formed strips to their designated conversion presses is to divide the tab press stock into individual strips and pass each strip through a tab press so that each tab press produces separate strips with one lane of formed lift-tabs in each strip. Singular tab dies may be provided within the tab press bed and substituted for the usual (multiple) tab forming die. Separate paths through the press as well as separate guide means which route the strips along the separate paths are necessary when using separate and individual tab formed strips, Each strip of stock material can be propelled through the tab press by a commercially available feeder such as a Ferguson Camtrol roll feed. A second roll feed can be inserted to propel the individual tab formed strips on to the designated conversion presses.
Presses for converting ends for cans and the like are known. Presses of this type are available from the Minister Machine Company of Minister, Ohio. U.S. Pat. No. 4,568,230 shows a layout of a press for processing workpieces into finished can ends with an opening tab attached thereto.
Presses used for the manufacture of easy-open can ends generally comprise a press bed mounted on legs which rest on the floor. Four columns or uprights are mounted on the press bed. The columns or uprights support a crown in which a main drive for the press components is mounted. The columns have slides attached therein for supporting a reciprocating main ram. The main ram carries the upper tooling of the main die set, which cooperates with lower tooling on the bed to make can ends from end stock workpieces. The main die set defines a plurality of stations in which the workpieces are progressively converted into easy-open can ends. A conveyor carries the workpieces into and through the stations of the die set. The tabs are formed by tab tooling, which is supplied with strip stock by a stock feed device. The tab tooling forms a tab and separates it from the strip stock at one station for attachment to a can end at another station.
The tab tooling has conventionally been mounted on the press bed laterally of the conveyor and laterally of the main die. The tab tooling may also be split so that it is arranged laterally on both sides of the main die. A bridge is required to transfer the tab stock strip across the main die set. Such an arrangement is shown in U.S. Pat. No. 4,568,230. The upper tooling is mounted on the main ram of the press.
One of the deficiencies associated with this arrangement of the tooling is that it is difficult to access the tooling for maintenance. Access to the can end tooling is difficult due to the presence of the tab tooling on one side of the main die and the tab tooling and tab stock feed device on the other side of the main die. The lateral placement of the tab tooling also increases the depth of the press from front to back. This requires a larger bed which increases the weight of the press and reduces its speed.
The present invention overcomes the disadvantages of the laterally-placed, split tab tooling by locating the tab tooling in another press where the only tooling is the tooling associated with the tab press. Placing the tab die set in another press allows full access to the main die from either the front or back of the press. Neither the tab tooling nor its stock device obstruct access to the main die set. This placement of the tab tooling also permits a reduction in the left to right width of the press between the columns and thus a reduction in weight of the press which allows the press to run at a higher speed. Another benefit of the tab tooling placement of the present invention is that it allows servicing of the tab die within the press. Still another benefit of placing the tab tooling and the can end tooling in separate presses is that there can be an additional tab press ready to go into production at any time the tab press in operation breaks down or needs to be shut down for repairs. The advantage of the present invention is increased productivity through higher operating speed and reduced down time for maintenance and tab press stock up.